Summarizing nodes in route propagation in auxiliary network for P2P overlay networks

ABSTRACT

Described herein is a method for creating route summaries in an auxiliary network for a peer-to-peer (P2P) overlay network for routing a data packet. The method comprises dividing a d-dimensional Cartesian space of nodes in the P2P overlay network into multiple virtual grids that form the auxiliary network, numbering each virtual grid, summarizing default overlay network zones of the P2P overlay network corresponding to each of the virtual grids that form the auxiliary network, receiving a data packet, and routing the data packet to a packet destination using one of the P2P overlay network and the auxiliary network.

RELATED APPLICATIONS

The following applications of the common assignee, incorporated byreference in their entirety, may contain some common disclosure and mayrelate to the present invention:

U.S. patent application Ser. No. 10/284,100 filed on Oct. 31, 2002entitled “AUTONOMOUS SYSTEM TOPOLOGY BASED AUXILIARY NETWORK FOR P2POVERLAY NETWORKS”; and

U.S. patent application Ser. No. 10/284,355 filed on Oct. 31, 2002entitled “LANDMARK NUMBERING BASED AUXILIARY NETWORK FOR P2P OVERLAYNETWORKS”.

FIELD OF THE INVENTION

This invention relates generally to peer-to-peer (“P2P”) overlaynetworks. In particular, the invention relates generally to summarizingroute propagation information in auxiliary networks for P2P overlaynetworks.

BACKGROUND OF THE INVENTION

Providing scalable and efficient content delivery is becoming moreimportant as the demand for applications such as streaming media isgrowing fast. Content Distribution Networks (“CDN”) and network serviceproviders, advocate using network overlays for providing scalable androbust Internet based applications. Typical overlays are administratorconfigured, and due to the centralized nature of the overlayconstruction process, it is not feasible to construct large overlays.

Recent application-level overlay networks, such as CAN, eCAN, Chord andPAST, are scalable and self-organizing in nature. Nodes in thesenetworks collectively contribute towards a fault-tolerant andadministration-free storage space. The basic functionality these systemsprovide is a distributed hash table (“DHT”). In these systems, an objectis associated with a key. Every node in the system is responsible forstoring objects whose keys map to the ID of the node (via hashing).Retrieving an object amounts to routing to a node that is responsiblefor storing that object. The routing path on these overlay networks isat the application-level rather than at the IP level.

While elegant from a theoretical perspective, these systems suffer fromat least two limitations. First, they rely on application-level routingthat largely ignores the characteristics of the underlying physicalnetworks. Because the underlying physical characteristics are not takeninto consideration, excessive routing delays typically result. Second,they construct a homogeneous structured overlay network, while inreality, the nodes usually have different constraints and capacitiessuch as storage, load, packet forwarding capacities and networkconnections.

In addition, overlay networks are typically constrained. In other words,the number of connections for a node is fixed or limited. Because of theconstraints, the ability to accurately model the underlying physicalcharacteristics is limited as well. Further, the earlier auxiliarynetworks do not handle the dynamic nature of the underlying networkwell, for example, when nodes exit or enter the network.

Still further, the amount of state information that needs to bemaintained in the overlay network may be excessive.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forcreating route summaries in an auxiliary network for a P2P overlaynetworks may include dividing a d-dimensional Cartesian space of nodesinto multiple virtual grids, numbering each virtual grid, andsummarizing default overlay network zones corresponding to each of thevirtual grids.

According to another embodiment of the present invention, a method foradvertising routing information using route summaries for an auxiliarynetwork for a P2P overlay network, wherein route summary includes ad-dimensional Cartesian space of nodes into multiple virtual grids anddefault overlay network zones are summarized into corresponding virtualgrids. The method may include determining a virtual grid ID for one ormore nodes of the overlay network corresponding to each of the one ormore nodes, determining a transport address for each of the one or morenodes; and advertising the virtual grid ID and the transport addresscorresponding to each of the one or more nodes.

According to yet another embodiment of the present invention, a methodfor routing using an expressway node based route summaries for anauxiliary network for a P2P overlay network, wherein route summaryincludes a d-dimensional Cartesian space of nodes into multiple virtualgrids and default overlay network zones are summarized intocorresponding virtual grids, the method may include receiving a packet,determining if a packet destination information is in a route summaryfor the expressway node, and routing the packet to the packetdestination if it is determined that the packet destination informationis in the route summary.

According to a further embodiment of the present invention, a method forrouting using ordinary node based route summaries for an auxiliarynetwork for a P2P overlay network, wherein route summary includes ad-dimensional Cartesian space of nodes into multiple virtual grids anddefault overlay network zones are summarized into corresponding virtualgrids. The method may include receiving a packet, determining if thepacket has been tagged to use a default overly for routing, and routingthe packet using the default overlay network if it is determined thatthe packet has been tagged to use the default overlay.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention will become apparent to those skilledin the art from the following description with reference to thedrawings, in which:

FIG. 1 is an exemplary diagram illustrating a conventional eCAN overlaynetwork;

FIG. 2 is an exemplary diagram illustrating the use of autonomous systemlevel topology to select expressway neighbors in a default overlayaccording to an embodiment of the present invention;

FIG. 3 is an exemplary diagram illustrating a landmark space accordingto an embodiment of the present invention;

FIG. 4 is an exemplary diagram illustrating an partitioning of Cartesianspace into grids according to an embodiment of the present invention;

FIG. 5 is a flow graph illustrating an exemplary method for summarizinga Cartesian space for route advertisement according to an embodiment ofthe present invention;

FIG. 6 illustrates a flow graph of an exemplary method for routingadvertisement of expressway nodes using virtual grids according to anembodiment of the present invention;

FIG. 7 illustrates a flow graph of an exemplary method for routing thatan expressway node may perform to route information packets according toan embodiment of the present invention; and

FIG. 8 illustrates a flow graph of an exemplary method for routing thatan ordinary node may perform to route information packets according toan embodiment of the present invention.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the principles of the presentinvention are described by referring mainly to exemplary embodimentsthereof. However, it is to be understood that the same principles areequally applicable to many types of auxiliary networks for P2P overlaynetworks.

In an embodiment of the present invention, an existing overlay network,such as CAN, eCAN, Tapestry, Chord, Pastry, and the like, may beaugmented with an auxiliary network to improve performance (for example,routing performance). The auxiliary network, also termed “expresswaynetwork”, allows the heterogenic conditions, i.e. the varyingcharacteristics of the underlying physical networks, to be exploited. Inthe expressway network, heterogenic conditions such as physicalproximity, forwarding capacity and connectivity of the nodes of thenetwork may be taken into account. Also, unlike the previous networks,the expressway network may be unconstrained, for example, in its storagecapacity of routing-information.

As mentioned above, examples of an overlay networks include CAN, eCAN,Pastry, and Chord. With CAN, the problem of data placement/retrievalover large-scale storage systems is abstracted as hashing that maps“keys” onto “values”. CAN organizes the logical space as a d-dimensionalCartesian space (a d-torus). The Cartesian space is partitioned intozones, with one or more nodes serving as owner(s) of the zone. An objectkey is a point in the space, and a node owns the object if it owns thezone that contains the point. Routing from a source node to adestination node boils down to routing from one zone to another in theCartesian space. Node addition corresponds to picking a random point inthe Cartesian space, routing to the zone that contains the point, andsplitting the zone with its current owner(s). Node removal amounts tohaving the owner(s) of one of the neighboring zone take over the zoneowned by the departing node. In CAN, two zones are neighbors if theyoverlap in all but one dimension along which they neighbor each other.

eCAN augments CAN's routing capacity with routing tables of larger span.Every k CAN zones represent an order-1 zone, and k order-i zonesrepresents an order-(i+1) zone. The variable k is called the zonecoverage factor. As a result, a node is an owner of a CAN zone and isalso resident of the high-order zones that encompass the CAN zone.Besides its default routing neighbors that are CAN zones, a node alsohas high-order routing neighbors that are representatives of itsneighbors in the high-order zones. eCAN provides flexibility inselecting the high-order neighbors. When selecting a representative fora high-order neighbor, a node may be selected that is closest to thecurrent node amongst all the nodes that belong to the neighboringhigh-order zone.

FIG. 1 illustrates an exemplary eCAN 100. The eCAN 100 includes defaultCAN zones 110, and in this example, each default CAN zone 110 is 1/16 ofthe entire Cartesian space. Also, four neighboring default zones 110make one order-2 eCAN zone 120. Thus, in this example, there are sixteendefault zones and four order-2 zones. While not shown, the neighboringorder-2 zones may be used to construct order-3 zones, order-3 zones usedto construct order-4 zones, and so on.

In addition, a node may own a particular default CAN zone. In thisinstance, the node 115 owns the CAN zone 110 in the upper left. Inaddition, a node is a resident of the higher order zones that encompassthe particular default zone. The routing table of node 115 includes adefault routing information of CAN (represented as arrows 140) that linkonly to the immediate neighbors of node 115. The routing table alsoincludes high-order routing information (represented as arrows 150 and160) that link to nodes of neighboring eCAN zones 120 and 130. In thisexample, node 115 may reach node 119 using eCAN routing (115, 117, 119).

In an embodiment of the present invention, using an auxiliary networklike the expressway network, the heterogeneity of nodes may berepresented without altering the overlay network like CAN and eCAN. Inother words, the characteristics of the underlying physical network istaken into consideration. However, it should be noted that theexpressway network may be used to augment many types of overlay networksand is not limited to CAN and eCAN.

In the expressway network, each node may establish connections to nodesin its physical proximity that are “well-connected” and have goodforwarding capacities. For example, routers and gateways and the nodesthat are near to the routers and gateways are better suited to forwardpackets. Forwarding capacities typically refers to network bandwidth andpacket processing abilities. These well-connected nodes are calledexpressway nodes. The expressway nodes themselves may be linked to otherexpressway nodes that are close by called expressway neighbors to forman expressway.

The expressway may be used to route information in the network. Notethat the number of expressway links from a particular expressway node toother expressway nodes is unconstrained. In other words, the number ofexpressway links established by each expressway node is arbitrary andmaybe different for each expressway node.

For a given default overlay network, such as eCAN, a correspondingexpressway network may be constructed in many different ways. While notexhaustive, the expressway nodes typically may serve the followingpurposes: (1) to propagate routing information when nodes join or leaveor when the network conditions change; (2) to resolve the routingdestinations; and (3) to forward information packets for multicasting orfor better IP routing performance.

As noted above, the auxiliary expressway network includes expresswaynodes. The expressway nodes may establish expressway connections amongsteach other. Typically, the expressway nodes establish connections withother expressway nodes that are “close” in network distance. Byestablishing expressways with other close expressway nodes, the routingperformance of the network may be improved. In a similar manner,ordinary nodes—i.e. the non-expressway nodes—also may establishconnections with expressway nodes that are close as well. In thismanner, data from any node—ordinary or expressway node—may be forwardedto the destination efficiently.

Distances may be measured in a variety of ways. While note exhaustive,the ways to determine distances include simple geographical distance,peak latency, average and mean latencies, number of autonomous systemhops, number of network hops, and the like.

In an embodiment of the present invention, expressway nodes determineand advertise or publish their positions—typically over the defaultoverlay network. A particular expressway node may determine itsproximity to other expressway nodes based on the published information.Based on the proximity information, the particular expressway node mayestablish expressway connections with other expressway nodes.

While not exhaustive, the following examples are some criteria thatdetermine when a particular expressway node may establish an expresswayconnection with one or more other expressway nodes. One example is thatthe particular expressway node may establish expressway connections witha pre-determined number of the closest other expressway nodes. Note thatthe pre-determined number may be one. Also note that the pre-determinednumber may be different for each expressway node, i.e. is arbitrary.Another example is that the particular expressway node may establishexpressway connections with all other expressway nodes that are within apre-determined distance from itself. Again, the predetermined distancemay be different for each expressway node.

Indeed, the criteria may be a combination. For example, an expresswaynode may always establish a pre-determined minimum number ofconnections, but may also establish connections with all otherexpressway nodes within a pre-determined distance.

Similarly, an ordinary node may determine its proximity to expresswaynodes based on the published positions. Based on the proximityinformation, each ordinary node may establish ordinary connections withexpressway nodes in a similar manner as described above. The criteriaused establish the ordinary connections may be individualized for eachordinary node.

The auxiliary expressway network may be constructed in a variety of waysincluding being based on autonomous system (“AS”) level topology andlandmark numbering. An autonomous system (or AS) may be viewed as anetwork or a group of networks under a common administration with acommon set of routing policies. FIG. 2 illustrates a diagram 200illustrating the use of AS topology to select expressway neighbors in adefault overlay, for example eCAN. The diagram 200 includes expresswaynodes 210-1 and 210-2. The diagram 200 also includes ordinary nodes220-1, 220-2 and 220-3. These nodes all belong to the same AS as theexpressway node 210-1. In addition, the diagram 200 also includesordinary nodes 230-1 and 230-2 which belong to the same AS as theexpressway node 210-2. Note that the expressway nodes establish anexpressway connection between themselves to form the expressway. Also,all ordinary nodes establish connections with expressway nodes in theirproximity. Further, each node of an AS establishes connections withother nodes in the same AS.

As noted above, landmark numbering may be used to form the expressways.In the expressway network utilizing landmark numbering, a plurality oflandmark nodes are chosen that are randomly scattered throughout anetwork, for example the Internet. An example of a landmark node may bea gateway server in Washington, D.C. and another may be a router in PaloAlto, Calif. The landmark nodes may be a part of the overlay network ormay be a standalone.

Each expressway node may determine its position relative to the landmarknodes by measuring its distance from each of the landmark nodes. Forexample, if there are n landmark nodes, then for a node A, the measureddistance from the node A to the landmark nodes may be represented by asequence <d₁, d₂, . . . , d_(n)> wherein d₁ is the distance from node Ato the first landmark node, d₂ is the distance from node A to the secondlandmark node and so on. The node A then may be viewed as beingpositioned in an n-dimension Cartesian space using the sequence <d₁>,d₂, . . . , d_(n)> as its coordinates. In other words, the landmarknodes serve as axis of the Cartesian coordinate system. This Cartesianspace is termed the landmark space. The nodes that are close to eachother should have similar landmark measurements.

FIG. 3 illustrates an exemplary landmark space 300 using three landmarknodes. As shown in FIG. 3, the three landmark nodes—landmark1, landmark2and landmark3—serve as the basis of the coordinate axes of the landmarkspace. The landmark space 300 includes two nodes n₁ and n₂ withcoordinates <d₁₁, d₁₂, d₁₃> and <d₂₁, d₂₂, d₂₃>, respectively. How closethe nodes n₁ and n₂ are to each other may be determined based on theirrespective coordinate values.

As indicated above, when an expressway node joins an expressway (orperiodically), it may advertise all the local nodes that are in itsphysical proximity to neighboring expressway nodes. Also, each ordinarynode may keep the addresses of the local expressway nodes and theexpressway nodes may maintain route summaries.

However, the number of entries in a route summary is typically on theorder of the number of nodes in the system. In a large network, theamount of information is likely to be large as well, and thus may becomeexpensive to maintain and difficult to keep the routing state current.Thus, it becomes desirable to reduce the routing states that the nodeshave to keep.

To reduce the amount of routing state information maintained at eachnode, routes may be advertised with summarization. In an embodiment ofthe present invention, the summarization is based on partitioning thed-dimensional Cartesian space into virtual grids. As an example, FIG. 4is a diagram 400 illustrating partitioning of a two-dimensionalCartesian space using 4×4 grids. As shown in FIG. 4, the two-dimensionalCartesian space is divided into 16 grids numbered from 0 to 15. Duringroute advertisement, a node advertises the grid ID that the node maps toas an indication of its position. For example, if the node's coordinateis {0.1, 0.3}, then the node would advertise the grid ID of 4.

FIG. 5 is a flow graph illustrating an exemplary method 500 forsummarizing a Cartesian space for route advertisement. As shown, thed-dimensional Cartesian space may be divided into multiple virtual grids(step 510). It is preferred that the grids are of equal size. Eachvirtual grid may be numbered, i.e. each virtual grid may be assigned avirtual grid ID (step 520). It is also preferred that the number ofgrids be m^(d), where d represents a dimensionality of the Cartesianspace and m is an integer. The grids may be numbered between 0 andm^(d)−1.

Also, the default overlay zones corresponding to the virtual grid IDsmay be summarized (step 530). Typically, each zone of the defaultoverlay, such as a CAN zone, may be summarized using the grid ID of thevirtual grid in which the center of the default zone falls. Note thatthe summarization is not limited to CAN and eCAN. As an example, for anyDHT-based overlays such as Pastry and Tapestry, the prefix or suffix ofthe nodes may be used to summarize the logical space. In an embodimentof the present invention, a summary can be a prefix (or suffix) of a setof nodes whose IDs in the P2P overlay share the same prefix (or suffix).A routing summary is generic and applicable to many types of P2Poverlay.

An algorithm for route advertisement using the virtual grids is similarto the standard distance vector algorithm. However, in an embodiment ofthe present invention, the following apply: (i) only expressway nodesmay participate in route advertisement; (ii) the node's transportaddress and the virtual grid that is used for summarizing the nodes maybe advertised; and (iii) the route advertisement messages may becontrolled with a time-to-live (“TTL”) value. The TTL value may controlhow far an advertisement can be propagated. Higher TTL values results inbetter performance but comes at a higher communication cost. The TTLvalue may be expressed as a number of expressway-node hops.

Having a small number of virtual grids would produce less preciseadvertised information. However, the benefit is that routing state thatan expressway node has to maintain becomes smaller as well. Even whenthe virtual grid is larger than the zone to be advertised, routing toany zone that belongs to the virtual grid guarantees that the target isinside the virtual grid and can be routed with the default overlyrouting in a bounded number of logical hops.

In an embodiment of the present invention, each ordinary node may keepthe address of the local expressway nodes and the expressway nodes maymaintain route summaries. The number of entries in the route summary ison the order of the number of virtual grids used for summarizing thenodes instead of being on the order of the number of nodes as disclosedabove.

FIG. 6 illustrates a flow graph of an exemplary method 600 to routeadvertisement for nodes using virtual grids. As shown in FIG. 6, atransport address, corresponding virtual grid ID, and a TTL value may bedetermined for a node (step 610). The node's transport address and thevirtual grid 11 may be advertised (step 620). Also, route summaries maybe maintained for the node (step 630). As noted above, typically, routesummaries are maintained for each expressway node.

Note that each expressway node may perform steps 610 and 620 toadvertise itself. Also, these steps may be performed by an externalentity for each of the nodes. Likewise, each expressway node may performstep 630 to maintain its own route summary or the summaries may bemaintained by an external entity and the expressway node may simplyaccess its corresponding summary as needed, such as when forwardingpackets of information.

FIG. 7 illustrates a flow graph of an exemplary method 700 for routingthat an expressway node may perform to route information packets. Asshown in FIG. 7, after receiving an information packet (step 710), theexpressway node may determine whether the packet destination is in theroute summary (step 720). If the packet destination is in the routesummary, then the expressway node may route the packet directly to thedestination (step 730).

If the packet destination is not in its route summary, then theexpressway node may determine if there is another expressway node thatis closer to the destination (step 740). If there is a closer expresswaynode, then the expressway node may forward the packet to the closer node(step 750). As discussed previously, the concept of distance may bedetermined in a variety of ways. Therefore, determining which node iscloser will be similarly varied.

If there is no closer expressway node, then the expressway node may usethe default overlay routing, such as CAN and eCAN, to route the packet(step 760).

FIG. 8 illustrates a flow graph of an exemplary method 800 for routingthat an ordinary node may perform to route information packets. As shownin FIG. 8, after receiving an information packet (step 810), theordinary node may determine whether the packet has been tagged to usethe default overlay routing (step 820). If so, the ordinary node mayused the default overlay routing to route the packet (step 830).

If the packet has not been so tagged, the expressway node may determineif the packet destination is to one of its neighbors (step 840). Forexample, the neighbor may in the same virtual grid ID, or the neighbormay a direct eCAN neighbor. A neighbor may be any node that the currentnode may directly forward the packet. If the destination is to one ofthe neighbors, then the ordinary node may forward the packet to theneighbor (step 850). If not, the ordinary node may forward the packet toan expressway node (step 860).

The combination of methods 700 and 800 guarantees that a packet willreach its destination. For example, if the destination is in the routesummary, the expressway will route the packet to the destination or to anode that is close to the destination. If the expressway routes thepacket to a node that is not the destination, from then on defaultrouting is used to route the packet. If the destination is not in theroute summary, again default routing is used.

While the invention has been described with reference to the exemplaryembodiments thereof, it is to be understood that various modificationsmay be made to the described embodiments of the invention withoutdeparting from the spirit and scope of the invention. The terms anddescriptions used herein are set forth by way of illustration only andare not meant as limitations. In particular, although the methods of thepresent invention has been described by examples, the steps of themethod may be performed in a different order than illustrated or may beperformed simultaneously. These and other variations are possible withinthe spirit and scope of the invention as defined in the following claimsand their equivalents.

1. A method for creating route summaries in an auxiliary network for apeer-to-peer (P2P) overlay network for routing a data packet, the methodcomprising: organizing a logical space of the P2P overlay network as ad-dimensional Cartesian space of nodes in the P2P overlay network havingdefault overlay network zones, each zone includes one or more of thenodes in the P2P overlay network; dividing the d-dimensional Cartesianspace of nodes in the P2P overlay network into multiple virtual gridsthat form the auxiliary network; numbering each virtual grid;summarizing the default overlay network zones of the P2P overlay networkcorresponding to each of the virtual grids that fort the auxiliarynetwork, wherein the step of summarizing includes: a) determining acenter of each of the default overlay network zones; and b) correlatingthe center of each of the default overlay network zones to acorresponding virtual grid where the center falls into; receiving a datapacket; and routing the data packet to a packet destination using one ofthe P2P overlay network and the auxiliary network.
 2. The method ofclaim 1, wherein the multiple virtual grids are of equal size.
 3. Themethod of claim 1, wherein the number of virtual grids is m^(d) whereind is a dimensionally of the Cartesian space and m is an integer.
 4. Amethod for advertising muting information using route summaries for anauxiliary network for a peer-to-peer (P2P) overlay network, wherein eachof the route summaries includes a d-dimensional Cartesian space of nodesof the P2P overlay network mapped into multiple virtual grids that formthe auxiliary network and default overlay network zones summarized intocorresponding to virtual grids of the auxiliary network, the methodcomprising: determining a virtual grid ID in the auxiliary network forone or more nodes of the P2P overlay network corresponding to each ofthe one or more nodes; determining a transport address for each of theone or more nodes; advertising and the transport address in theauxiliary network corresponding to each of the one or more nodes; andmaintaining route summaries based on the advertised routing information,wherein the route summaries are maintained only for expressway nodes inthe auxiliary networks.
 5. The method of claim 4, further comprisingdetermining a time-to-live (TTL) value for each of the one or morenodes.
 6. The method of claim 5, wherein the TTL value for each of theone or more nodes is expressed as a number of expressway hops.
 7. Themethod of claim 5, further comprising using the TTL value to control apropagation distance for an advertisement can be propagated.
 8. A methodfor routing using an expressway node based route summary for anauxiliary network for P2P overlay network, wherein route summaryincludes a d-dimensional Cartesian space of nodes into multiple virtualgrids and default overlay network zones are summarized intocorresponding to virtual grids, the method comprising: receiving apacket; determining if a packet destination information is in a routesummary for the expressway node; routing the packet to the packetdestination if it is determined that the packet destination informationis in the route summary; determining if another expressway node iscloser to the packet destination if it is determined that the packetdestination information is not in the route summary; forwarding thepacket to the another expressway node if it is determined that theanother expressway node is closer to the packet destination; and routingthe packet using the default overlay network if it is determined thatthe another expressway node is not closer to the packet destination. 9.A method for routing using an ordinary node based route summary for anauxiliary network for a P2P default overlay network, the methodcomprising: providing the route summary that includes a d-dimensionalCartesian space of nodes in the default overlay network mapped intomultiple virtual grids in the auxiliary network and default overlaynetwork zones of the default overlay network summarized intocorresponding virtual grids; receiving a packet; determining if thepacket has been tagged to use the default overlay network for routing;and routing the packet using the default overlay network upon thedetermining that the packet has been tagged to use the default overlaynetwork zones in the default overlay network; otherwise, routing thepacket using the multiple virtual grids in the auxiliary network. 10.The method of claim 9, further comprising: determining if packetdestination is a neighbor node of the ordinary node; and forwarding thepacket to the neighbor node if it is determined that the neighbor nodeis the packet destination.
 11. The method of claim 10, furthercomprising forwarding the packet to an expressway node if it isdetermined that the neighbor node is not the packet destination.
 12. Themethod of claim 10, wherein the neighbor node is at least one of:another node in the same virtual grid Id of the ordinary node; anothernode that is a direct neighbor in the default overlay; and another nodethat may receive packets directly from the expressway node.